Vegard's Law in KFe(S1-xSex)2

The lattice constant and chemical composition of a specimen of a mixed crystal can be determined simultaneously on the basis of well-established single-crystal X-ray diffractometry. From the data for various compositions of the system, the relation between the two quantities, which usually follows Vegard's law, can be established. An example of the application of this procedure is shown for the case of mixed crystals KFe(S1-xSex)2 (0≤x≤1). In contrast to a nonlinear relation to the nominal composition, the lattice constants are found to be linear to the composition when it is properly determined.